1. Field of the Invention
The present invention relates to a toner cartridge and an image forming apparatus to be mounted with the toner cartridge.
2. Description of the Related Art
A toner cartridge of the prior art essentially includes a toner bottle having a toner outlet port and an outlet port shutter, and a rotation member attached to the toner bottle in a rotatable manner (see, for example, Japanese Unexamined Patent Publication No. 2003-316138). When the toner cartridge is inserted into an image forming apparatus along its length, the toner bottle is unlocked from the rotation member, and a gear of the rotation member is engaged with a gear of a developing device of the image forming apparatus. When an user thereafter rotates the rotation member in a predetermined direction, the outlet port shutter of the toner bottle coupled to the gear and an inlet port shutter of the developing device coupled to the outlet port shutter are simultaneously opened.
Image forming apparatuses such as a copying machine, a facsimile machine and a printer utilizing an electrophotographic system typically include a photosensitive drum on which an electrostatic latent image is formed by laser irradiation means or the like, and a developing device provided in the vicinity of the photosensitive drum for developing the electrostatic latent image with toner. In such an image forming apparatus, a toner cartridge is removably mounted for supplying the toner to the developing device.
Where the developing device employs a two-component developing agent containing a toner and a carrier such as iron powder, for example, the toner and the carrier are stirred to be homogeneously mixed in a stirring chamber, and the resulting two-component developing agent is transported to the vicinity of a developing roller incorporating a magnetic member.
The developing agent transported to the vicinity of the developing roller is carried on a surface of the developing roller by a magnetic field of the developing roller to provide a so-called magnetic brush. When the magnetic brush is brought into opposed relation to the photosensitive drum, only negatively charged toner is transferred onto the photosensitive drum to develop the electrostatic latent image. When the carrier separated from the toner thereafter passes through a repulsive magnetic field of the developing roller, the carrier falls back into the stirring chamber of the developing device.
Therefore, the toner concentration of the developing agent in the developing device is gradually reduced during repeated image formation. When the toner concentration is reduced to a predetermined concentration level, the reduction is detected by a sensor provided in the developing device. In response to the detection, a toner bottle of the toner cartridge is rotatively driven, whereby the toner is supplied to the developing device from a toner outlet port of the toner bottle. When the toner concentration is recovered to the predetermined concentration level, the driving of the toner bottle is stopped.
The amount of the toner in the toner bottle is also reduced during repeated supply of the toner. When the toner bottle is substantially emptied, a message for replacement of the toner cartridge is displayed on an operation panel of the image forming apparatus or the like to prompt a user to replace the toner cartridge.
Since the toner is very fine powder, a very small amount of toner remains in the toner bottle substantially emptied. Therefore, the toner bottle is not completely emptied. In order to prevent the toner from leaking from the toner outlet port in the replacement of the toner cartridge, the toner cartridge generally has a shutter of a certain configuration provided on the toner outlet port.
In the case of the toner cartridge disclosed in Japanese Unexamined Patent Publication No. 2003-316138, the toner bottle is unlocked from the rotation member and the gear of the rotation member is engaged with the gear of the developing device by the insertion of the toner cartridge, and then the rotation member is rotated in a predetermined direction to simultaneously open the outlet port shutter coupled to the gear and the inlet port shutter coupled to the outlet port shutter. However, the opening and closing of the shutters is achieved by the engagement of the gears. This complicates the construction, and increases the costs. Where the toner cartridge is frequently mounted and demounted, the durability of the gears is unsatisfactory.
The engagement of the gears for the opening and closing of the shutters does not give a positive tactile feedback to the user, even if the toner cartridge is properly mounted with the shutters being fully opened by the operation of the rotation member. If the user fails to recognize that the toner cartridge is properly mounted, the user will make an attempt to further rotate the rotation member to break the gears and the like.